What I don't understand, though, is that a big spider hanging in a web is probably likely to scare off not only predators, but prey as well. What self-respecting insect is going to fly straight past a big spider? Surely evolution must have "taught" them by now that where a big spider is floating in mid-air, there's probably a web around it?

And what about predators interested in eating big spiders?

On the other hand, this construction may actually be quite effective in keeping big, clumsy animals like, say, humans, from destroying the web accidentally. Maybe that outweighs the visibility to prey.